Silicon integrated circuits have dominated the development of electronics, and many technologies based upon silicon processing have been developed over the years. Their continued refinement led to nano-scale feature sizes that can be important for making metal oxide semiconductor CMOS (complementary metal-oxide semiconductor) circuits. Silicon can be used as an optical medium, particularly for light having a wavelength of about 1.55 microns (μm). Light having a wavelength of 1.55 μm is often used for fiber-optic telecommunication systems. Some silicon devices have both electronic and optical components.